Various types of valve systems have long been known which control the passage of an incoming fluid towards containers or along circuits in general. Naturally, also known are the relative actuating systems that allow the activation and the management of the sections of passage in all the intermediate positions between the “completely open” status and the “closed” status.
The actuators currently employed in applications of control of flow with quarter-turn valves are constituted by a crank and slotted link mechanism, which converts a linear motion in a quarter-turn rotary motion. The trigger of the linear motion takes place by injection of air or oil in a chamber of a cylinder connected to the crank and slotted link. In many cases, a spring assembly is also inserted, also connected to the crank and slotted link and employed for guaranteeing a safety position in case a breakdown of either the electrical or pneumatic/hydraulic feeding is verified.
The simplicity and the robustness of the crank and slotted link actuator have rendered the most widespread system as far as the actuation of shut-off valves (on-off) is concerned.
On the contrary, a crank and slotted link conversion system has absolutely inadequate features in terms of precision of control, linearity, absence of clearances in stroke. These features, in part negligible in an on/off valve, result to be determining in a control valve, that is a valve with which the width of the section of passage wants to be controlled with precision in such a way as to control the fluid flow rate inside the circuit.
The present invention wants to overcome the limits of the current state of the art, by introducing an actuator capable of lengthening the life in exercise of the plants and for the minimization of the maintenance interventions. All this implies the need to improve the performance of such apparatuses, therefore to reduce the possibility of formation of clearances and lower the contribution of the friction forces.
The best way to increase the efficiency of such actuators is to linearize the gear ratios of the actuating torques, a feature that is always desirable for any mechanical system.
A type of actuator capable of satisfying at least in part said requisite is, for example, described in patent publication U.S. Pat. No. 3,267,816.
The system takes advantage of the sending in pressure of fluid, for example oil, in order to move pistons.
In particular, such a type of actuator is in a box-like shape and foresees a receiving chamber 13 inside of which a rotatable shaft 50 is passing on which a crown gear 14 is connected. Such a chamber 13 is in fluid communication with two conduits placed between them in parallel and inside of which, in each one, a double-effect sliding piston (pistons 15 and 16) is foreseen. The two pistons work in an antagonist manner. Each conduit, thanks to the presence of the sliding pistons, results to be subdivided into two parts, one that is addressed towards the chamber 13 and the other one that is addressed towards a source of fluid in pressure.
The pistons are then connected between them through a chain that engages with the crown gear connected around the rotatable shaft.
In such a manner, a translation of a piston, through the sending of oil in pressure, allows to drag in translation also the other piston and, consequentially, the chain put in motion causes the rotation of the crown gear.
The rotation of the crown gear, in turn, determines the rotation of the shaft on which it is connected.
The shaft is naturally connected to the valve in such a way that its rotation in a direction determines its opening, while a rotation in the opposite direction determines its closure.
In this way, therefore, the controlled inlet of oil in pressure in a conduit or in the other one allows to control an opening/closure of the valve system to which such a controller is associated.
However, this solution is not exempt from technical problems.
In the first place, a chain gear system is used. Such a solution, in general, is unreliable in time since the chain links of the chain can wear until breaking or can modify their reciprocal distances or sizes. In that case, a perfect grip would not be guaranteed anymore between the teeth of the gear and the space of the link inside of which the tooth of the crown has to be inserted. For that reason, it is possible to have a malfunctioning condition, efficiency losses and even a total block of the valve due to the breakage of the chain and/or of a crown tooth.
Further disadvantages linked to the use of a gear transmission are that of presenting a localized wear on a limited number of teeth and/or of an imprecision in the control deriving from the nature itself of the gear system used.
A further document is, for example, publication EP1903198 that describes a movement system in opening/closure of a throttle for the system of vehicle exhaust.
In this case, there is the need for moving the valve in opening and in closure through a mechanical system that is not cumbersome and that is unbound from the presence of low pressure. To this aim, an actuator in the form of a rotary electric engine is used which is installed at a distance with respect to a pulley on which the control axis of the rotation of the valve is connected. Such a pulley is brought in rotation through two wires that are fixed by an end to the pulley and by the other end to such a rotary engine. According to the rotation of the engine in a direction or in the opposite direction, such a rotation is transmitted through the wires to the pulley that thus rotating as well conducts the valve in opening and in closure.
The use of a rotary electric engine as actuator, in the place of the linear feeders, is not functional for different reasons.
There are, in fact, wear problems of the teeth, problems of recovery of the clearances and above all of encumbrance in the case of elevated torques. In many industrial applications, in fact, the value of the pair to transmit would not allow the use of such rotary engines.
In fact, in order to transmit relevant torques of opening, a direct application (“Direct-Drive”) becomes necessary, with costs and sizes that are probably unacceptable. Alternatively, a further reduction stage can be interposed between rotary engine and load, but also in this case there arise problems relative to the size of the reducer operating with very small rotations, inferior to the turn with consequent wear problems of the teeth and recovery of the clearances of the device. Further, the reducer interposed creates not insignificant problems.
A further document, which corresponds to the pre-characterizing part of the invention, is instead publication DE1750935, which describes two linear feeder conduits which generate an antagonist linear motion. The linear motion is then transmitted to a pulley on which a movement axis is connected that can be, for example, an axis of a valve. The gear takes place through a chain that engages in the pulley specifically teethed (therefore in the form of a sprocket), the whole with the same inconveniences already mentioned. In a variant, always of publication DE1750935, the use of a belt is described which however drags in rotation the pulley by friction. The text suggests, in fact, the use of friction gaskets that tend to increase the friction between the flat surface of the pulley and the belt, thus reducing the slidings.
It is evident, however, that such a solution is not functional since the belt anyway would tend to slip on the pulley, even if in a minimal way, therefore not guaranteeing a precision of movement of the valve. Moreover, such a solution requires often a registration of the belt in such a way as to guarantee always, during all the exercise, a fair coefficient of friction that eliminates any scraping. Last, being anyway the reciprocal sliding always present, this implies an early wear of the belt with a continuous need for maintenance/substitution of the same.